Stack damper

ABSTRACT

A damper comprising a duct defining an air flow path, opposing damper blades pivotally mounted within the duct, each damper blade having an end that is pivotally mounted in cantilevered fashion in the duct so that an opposing end is free to move within the duct, wherein each damper blade is planar in shape, cooperating flow straightening members disposed centrally in the air flow path, an air flow sensor for generating a signal cooperatively disposed between the flow straightening members, and an actuator for pivoting each damper blade within the duct in response to the signal from the air flow sensor to vary the damper blade position and thereby maintain a desired velocity of air exiting the damper.

FIELD OF THE INVENTION

The invention relates to a stack damper, and more particularly, to a stack damper which automatically maintains a downstream air flow velocity by adjusting a damper blade position in response to an air flow signal.

BACKGROUND OF THE INVENTION

Suitable air flow velocity is a widely accepted means of maintaining entrainment of air borne contaminants. To this end various environmental rules require that air exiting from an exhaust stack or duct be discharged into the air at a predetermined height (or some calculated distance from intake ducts) and a predetermined velocity to ensure proper diffusion.

One problem presented by this regulatory regime is the large constant volume of air which must be discharged to maintain proper velocity.

Compounding the problem is the volume of air which is required to be discharged varies during the day. For instance, the volume of discharged air could be reduced dramatically during off hours. On the other hand, regulations often require the velocity of discharged air to remain the same throughout the day. This often requires that ambient air be pumped into the stack to ensure constant discharge velocity. This in turn substantially increases the associated energy costs required to run the facility, even though the percentage of entrained contaminants may be very small.

It would be advantageous if the energy costs associated with the maintenance of a high velocity discharge could be reduced by reducing the amount of ambient air required to maintain the desired discharge velocity.

Representative of the art is U.S. Pat. No. 6,071,188 (2000) which discloses an exhaust system has an air exhaust duct having a charge opening and a discharge opening and defining an air flow path. A damper is mounted in the duct for maintaining a constant air velocity for air exiting the discharge opening. The damper has opposing damper blades pivotally mounted within the duct. Each damper blade has an end that is pivotally mounted in cantilevered fashion within the duct so that an opposing end is free to move within the duct. Each damper blade is parabolic in shape and minimizes the air turbulence over the damper blade and reduces vibration. Each damper blade can be pivoted in response to a change in air volume discharged through the discharge opening to maintain a desired velocity of air through the discharge opening.

What is needed is a stack damper which automatically maintains a downstream air flow velocity by adjusting a damper blade position in response to an air flow signal. The present invention meets this need.

SUMMARY OF THE INVENTION

The primary aspect of the invention is to provide a stack damper which automatically maintains a downstream air flow velocity by adjusting a damper blade position in response to an air flow signal.

Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings.

The invention comprises a damper comprising a duct defining an air flow path, opposing damper blades pivotally mounted within the duct, each damper blade having an end that is pivotally mounted in cantilevered fashion in the duct so that an opposing end is free to move within the duct, wherein each damper blade is planar in shape, cooperating flow straightening members disposed centrally in the air flow path, an air flow sensor for generating a signal cooperatively disposed between the flow straightening members, and an actuator for pivoting each damper blade within the duct in response to the signal from the air flow sensor to vary the damper blade position and thereby maintain a desired velocity of air exiting the damper.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention.

FIG. 1 is a plan view of the damper.

FIG. 2 is a perspective view of the damper.

FIG. 3 is a side view of the damper.

FIG. 4 is a side view of the damper.

FIG. 5 is cross sectional view 5-5 from FIG. 4.

FIG. 6 is a cross sectional view of the air flow measurement device.

FIG. 7 is a chart showing average air velocity as a function of distance from the stack damper.

FIG. 8 is a chart showing average air velocity as a function of distance from the stack damper.

FIG. 9 is a chart showing average air velocity as a function of distance from the stack damper.

FIG. 10 is a schematic representation of an example system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a plan view of the damper. Damper 100 comprises a duct defining an air flow path and generally having sides 10, 11, 12, and 13 arranged in any form suitable for installation in air handling system ductwork. Sides 10, 11, 12, 13 are connected together in a substantially air tight manner to avoid air leakage. Mounting member 14 is attached to side 10. An end of air piston 20 is connected to mounting member 14. Sides 10, 11, 12, 13, 14 and skirt 15 and flange 16 preferably comprise galvanized metal, but may also comprise any other material suitable for HVAC service. Portion 18 is disposed between sides 10, 11, 12, and 13 and skirt 15.

Damper blade 50 is attached in a cantilever fashion to damper shaft 30. Damper blade 51 is attached in a cantilever fashion to damper shaft 40. Vane 52 is fixedly connected between sides 10 and 13. Vane 52 is fixedly connected between sides 10 and 13. Vanes 52 and 53 are substantially parallel. Damper blades 50 and 51 are substantially parallel. Damper blades 50, 51 and vanes 52 and 53 are substantially flat (planar).

Damper blades 50 and 51 move in unison and express substantially the same position with respect to the air flow through the damper.

FIG. 1 illustrates the damper closed position. In the “closed” position the discharge area of the damper is not fully taken to zero air flow (0 CFM). Instead, the discharge area is in the range of approximately 40% to approximately 60% of the fully open discharge area. This has the effect of maintaining a suitable air flow velocity (FPM) for a suitable distance downstream of the damper during periods of reduced air flow rate (CFM). Of course, the position of damper blades 50 and 51 may be adjusted in the range of movement between fully open and the “closed” position depending upon the air flow requirements at the time.

Air flow measuring sensor 60 is disposed between vanes 52 and 53. Sensor 60 senses air flow through the damper. Vanes 52 and 53 act as air flow straightening members to improve the measurement accuracy of sensor 60 by reducing turbulence near the sensor. Vanes 52, 53 are substantially parallel to the air flow direction. Vanes 52 and 53 also serve to reduce turbulence and vibration in the duct caused by damper blades 50, 51 when they are in the partially closed or closed position.

FIG. 2 is a perspective view of the damper. Vanes 52 and 53 are not moveable in the preferred embodiment, but in an alternate embodiment some movement may be desirable to adjust air flow characteristics.

FIG. 3 is a side view of the damper. Damper 100 comprises sides 10, 11, 12, and 13 arranged in any form suitable for installation in air handling system ductwork. Sides 10, 11, 12, 13 are connected together in a substantially air tight manner to avoid air leakage. Mounting member 14 is attached to side 10. An end of air piston 20 is connected to mounting member 14. Sides 10, 11, 12, 13, 14 and skirt 15 and flange 16 preferably comprise galvanized metal, but may also comprise any other material suitable for HVAC service.

Skirt 15 and flange 16 are attached to an end 17 of the damper in an air tight manner to avoid air leakage. Flange 16 receives fasteners such as bolts to attach the damper to ductwork (not shown).

Linkage arm 21 is connected to a damper shaft 30. Linkage arm 22 is connected between damper shaft arm 23 and damper shaft arm 24. Damper shaft arm 24 is connected to damper shaft 40.

Actuator 20 moves the damper blades 50, 51. Actuator 20 may comprise any suitable device known in the art, including an electric motor or air piston. In this embodiment, air piston 20 is connected to a pressurized air source (not shown) and controller 603, see FIG. 10. As air piston 20 extends and retracts it actuates linkage 21 and thereby damper shaft 30 and damper shaft 40.

FIG. 4 is a side view of the damper. Flange 16 mates up to adjacent system ductwork.

FIG. 5 is cross sectional view 5-5 from FIG. 4. Damper blade 50 and 51 are shown in the “Closed” position. Air flow measuring device 60 is disposed between vanes 52 and 53.

FIG. 6 is a cross sectional view of the air flow measurement device. Device 60 comprises a static pressure measuring chamber 61 and a total pressure measuring chamber 62. Relative air flow is as shown in the figure. Air flow is a function of the differential pressure between chambers 61 and 62. Instruments known in the art (not shown) are connected to each chamber to measure the differential pressure, for example, the Honeywell model P7640A differential pressure sensor, see 601 in FIG. 10.

FIG. 7 is a chart showing average air velocity as a function of distance from the stack damper. With the damper at full open, the average velocity at a distance of 20 feet from the damper discharge is approximately 1180 FPM. The measured air flow is approximately 8866 CFM through a representative stack damper.

FIG. 8 is a chart showing average air velocity as a function of distance from the stack damper. With the damper at full open but at 60% of the air flow as in FIG. 7 (˜5319 CFM), the average velocity at a distance of 20 feet from the damper discharge is approximately 890 FPM. This represents approximately 80% of the velocity for the full open configuration in FIG. 7, but at only 60% of the air flow for FIG. 7.

FIG. 9 is a chart showing average air velocity as a function of distance from the stack damper. With the damper at 50% open and at 60% of the air flow as in FIG. 7 (˜5319 CFM), the average velocity at a distance of 20 feet from the damper discharge is approximately 865 FPM. This represents approximately 79% of the velocity for the full open/full flow configuration in FIG. 7.

FIGS. 7, 8 and 9 illustrate the capability of the stack damper to maintain appropriate air flow velocities in a stack system at reduced damper openings and air flow rates. For example, the stack damper would be used to maintain air flow velocities during off hour system operation such as during evening hours in an office building.

FIG. 10 is a schematic representation of an example system. Device 60 is connected to the differential air pressure sensor 601 by tubing 61, 62. Sensor 601 is electrically connected to a programmable controller 602 as required by the controller instructions (known in the art). Programmable controller 602 is connected to a motor or piston air pressure controller 603 (as described by the controller 602 and 603 instructions known in the art). Controller 603 is connected to piston 20 by pneumatic lines 27, 28 as shown in FIG. 3. Table 604 describes some of the information that can be obtained from the programmable controller 602 for other system uses. Controller 603 is operatively connected to the sensor 60 and the actuator 20 for automatically controlling pivotal movement of each damper blade 50, 51 in response to the measured change in the air flow so as to maintain a substantially constant discharge air velocity from the damper.

Although a form of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts without departing from the spirit and scope of the invention described herein. 

1. A damper comprising: a duct defining an air flow path; opposing damper blades pivotally mounted within the duct, each damper blade having an end that is pivotally mounted in cantilevered fashion in the duct so that an opposing end is free to move within the duct, wherein each damper blade is planar in shape; cooperating flow straightening members disposed centrally in the air flow path; an air flow sensor for generating a signal cooperatively disposed between the flow straightening members; and an actuator for pivoting each damper blade within the duct in response to the signal from the air flow sensor to vary the damper blade position and thereby maintain a desired velocity of air exiting the damper.
 2. A damper according to claim 1 wherein said actuator comprises a pneumatic piston engaged with a damper blade shaft.
 3. The damper according to claim 1 further comprising a controller operatively connected to the sensor and the actuator for automatically controlling pivotal movement of each damper blade in response to the measured change in the air flow so as to maintain a substantially constant discharge air velocity. 